The bearing assembly which supports a shaft and sleeve for relative rotation is of critical importance to the lifetime and stability of a motor, gyroscope or other devices based on relative rotation. However, ball bearing assemblies have many mechanical problems such as wear, run-out and manufacturing difficulties. Moreover, resistance to operating shock and vibration is poor, because of low damping. Thus, there has been a search for alternative bearing assemblies.
One alternative bearing design which has been investigated is a hydrodynamic bearing. In a hydrodynamic bearing, a lubricating fluid such as gas or a liquid provides a bearing surface between a fixed member of the housing and a rotating member of the disc hub. Typical lubricants include oil or ferromagnetic fluids. Hydrodynamic bearings spread the bearing interface over a large continuous surface area in comparison with a ball bearing assembly, which comprises a series of point interfaces. This is desirable because the increased bearing surface reduces wobble or run-out between the rotating and fixed members. Further, improved shock resistance and ruggedness is achieved with a hydrodynamic bearing. Also, the use of fluid in the interface area imparts damping effects to the bearing which helps to reduce non-repetitive runout.
However, to design an effective self-contained fluid dynamic bearing, the issue of fluid retention must be addressed. If fluid is lost during operation of the bearing, or in the event of shock, then the effectiveness of the bearing is diminished or lost.